Comments and opinions please.
I have been examining my collection of Dowty Oleomatic forks bits & bobs with a view to bringing them back to life.
Whilst there are some minor signs of wear there is little sign of ovality in the bronze bottom bushes so that it came as a bit of a surprise that the bushes measured up at 1.515” diameter, that is to say 0.015” oversize on the 1.5” diameter of the bottom tubes. The two-part fibre bushes that sit just above the piston seals proved to be 1.600” diameter, that is to say 0.025” undersize on the 1.625” bore of the top tubes. All these sizes seem fairly consistent between the various parts in my possession.
Unless I am reading it wrong the split fibre bush is effectively the only thing of any solidity to hold concentric the top end of the lower tube, any contribution by the flexible piston seal notwithstanding. If this is so then it is surely yet another reason why it is possible to loose air pressure! With a clearance of 15 thou at the bottom and 25 at the top the technical term “ flopping about like a p***k in a top hat” springs to mind, those poor old seals have enough to do without trying to keep the tubes concentric as well in all conscience!
So my questions are:
Is the clearances mentioned above anything like normal for the Dowty forks?
Has anyone rebuilt a set and if so what clearances did you use?
When working properly the Dowty forks are said to give a good ride, if so is this degree of clearance noticeable on the road?